For example, control constant identification systems include:
(1) an identification system which changes a torque command for changing the rotation speed and calculates torque command integration amount and rotation speed change width, then performs an operation of (inertia)=(torque command integration amount)/(rotation speed change width) for finding inertia (see Japanese Patent Unexamined Publication No. Sho 61-88780); PA1 (2) an identification system which inputs a speed command having a lamp section, executes a speed loop under P control, and finds load inertia from the ratio between steady speed deviation in a state in which no load inertia exists and that in a state in which load inertia exists (see Japanese Patent Unexamined Publication No. Hei 6-70566); and PA1 (3) an identification system which time-integrates actual and simulated current detection values or current command values for finding a current area and corrects an initial inertia assumption value from the current area calculation result, thereby finding inertia (see Japanese Patent Unexamined Publication No. Hei 4-325886). PA1 a command generation section for generating a speed command Vref; PA1 a speed control section for determining a torque command Tref by the speed command Vref and actual motor speed Vfb and controlling motor speed; PA1 an estimation section for simulating the speed control section according to a model and outputting an estimated torque command Tref'; and PA1 an identification section for identifying inertia J according to a ratio between a value STref resulting from time integration of the torque command Tref output by the speed control section at a predetermined interval [a, b] and a value STref' resulting from time integration of the torque command Tref' output by the estimation section at the predetermined interval [a, b], characterized in that PA1 the predetermined interval [a, b] and the speed command Vref are set so that the actual motor speed Vfb and motor speed Vfb' found by the estimation section become the same non-zero values at the time b.
However, conventional examples (1), (2), and (3) have a problem that inertia identification value errors or variations are large if viscous friction or Coulomb's friction exists. The following problems are also involved: Particularly in (1), commands are limited to those for changing the rotation speed at a given rate; in (2), the effect of disturbance is easily received because integration control is not performed; and in (3), inertia is found while fuzzy inference, etc., is used to repeat a correction so that the initial inertia assumption value approaches the actual inertia, thus resulting in large amounts of complicated operations.